1. Field of the Invention
This invention relates to an image pickup apparatus which corrects hand shake to thereby improve the accuracy of a picked-up image, the camera main body thereof and an interchangeable lens.
Particularly it relates to an image pickup apparatus which achieves an improvement in correcting performance for hand shake, the camera main body thereof and an interchangeable lens.
2. Related Background Art
In the present day cameras, operations important to photographing such as exposure determination and focusing are all automated and the possibility that even a person unskilled in camera operation causes failure in photographing has become very rare.
Also, recently, a system for preventing a hand shake applied to a camera has also been studied, and factors inducing a photographer's error in photographing has become almost null.
An image stabilizer system for preventing hand shake will be briefly described here.
The hand shake of a camera during photographing is usually a vibration of a frequency of 1 Hz to 10 Hz. To enable a photograph free of image blur to be taken even if such a hand shake is present at the point of time of exposure, it is necessary to detect the vibration of the camera due to the hand shake, and displace a correction lens in a plane orthogonal to the optical axis thereof in conformity with the result of this detection (optical image stabilizer system).
That is, to take a photograph free of image blur even if the vibration of the camera occurs, firstly, it becomes necessary to accurately detect the vibration of the camera, and secondly, to correct a change in the optical axis due to a hand shake.
The correction of image blur is effected by detecting the vibration of the camera by an angular velocity sensor or the like, and driving a correcting optical apparatus for making the photographing optical axis eccentric on the basis of the detected information of the vibration of the camera (see, for example, Japanese Patent Application Laid-open No. H07-218967).
Also, in order to improve the accuracy of the correction of image blur during close-up photographing in which the photographing distance is short, there has been proposed an apparatus which carries an acceleration sensor and an angular velocity sensor thereon, and detects not only rotation vibration, but also parallel vibration and corrects the both vibrations (see, for example, Japanese Patent Application Laid-open No. H03-46642).
Also, when the acceleration sensor is used, there may occur an error arising from the detection of parallel vibration due to the influence of gravity acceleration. Therefore, there has also been proposed an apparatus which calculates the coordinate conversion matrix of a stationary coordinates system and a camera coordinates system from the signal of a six-axis sensor (the acceleration of XYZ axes and an angular velocity about each axis), and eliminates the influence of the gravity acceleration (see, for example, Japanese Patent Application Laid-open No. H09-80523).
In a case where as disclosed in Japanese Patent Application Laid-open No. H09-80523, the six-axis sensor is used to effect posture calculation and effect the elimination of the gravity acceleration component of the acceleration sensor, the construction becomes complicated.
It results in the necessity of the larger scale and increased cost of the system, and a high-speed calculation processing system.
As a method of cutting a DC component caused by the gravity, there is a method of inserting a high-pass filter to thereby cut a DC component.
Here, description will specifically be made of the influence on which the detection of parallel vibration the gravity acceleration has.
In a state as shown, for example, in FIG. 9A the accompanying drawings wherein a conventional camera is leveled at a regular position, an acceleration sensor 92 outputs a signal corresponding to the gravity acceleration G.
When parallel vibration is to be detected, this gravity acceleration component is cut by a high-pass filter (HPF) and integration is effected twice (two integrations), whereby parallel vibration displacement can be calculated.
However, when as shown in FIG. 9B of the accompanying drawings, the camera is inclined at an angle α from the regular position, the gravity acceleration component of the acceleration sensor 92 changes from G to G cos α.
This amount of change is also cut by the HPF, but the HPF has the characteristic that it must detect a hand shake component and therefore, it is necessary to set the cut-off frequency to a low level (e.g. 0.05 Hz).
Accordingly, in the conventional camera, when a DC component caused by gravity acceleration has changed, a long time is required until the amount of change is completely cut and an output signal becomes stable. As the result, the accuracy of the correction of image blur may be lowered.